1. Field of the Invention
The present invention relates to a test of cell conductivity, and more particularly to a test method of cell conductivity on a communication path in an ATM switching system and an apparatus for the same.
2. Description of the Related Art
A conventional cell conductivity test apparatus adaptive for an ATM switching system is proposed in, for example, Japanese Laid Open Patent Disclosure (JP-A-Heisei 6-268668). In the proposed cell conductivity test apparatus, a cell conductivity test circuit of a communication path is composed of a test cell generating unit for generating at a arbitrary rate test cells each of which has a cell header indicative of a destination address and a switching routing tag for sending out the test cell to a switch section, a test cell collecting section for collecting the test cells which are turned around by a line correspondence section in the communication path, and a test cell check section for testing the collected test cells. The cell conductivity test circuit is connected to the switch section in the communication path. A control unit performs the routing to the line correspondence section. In this manner, in the conventional cell conductivity test apparatus, the test cells can be sent out at an arbitrary rate, and a special test route of a specific portion can be tested individually.
The conventional cell conductivity test apparatus of an ATM switching system will be described below with reference to FIG. 1. As shown in FIG. 1, a test cell generating unit 1 generates test cells at an arbitrary rate. The generated test cells are supplied to an input buffer server 2. Normal cells which are used to transmit speech or data are also supplied to the input buffer server 2. The input buffer server 2 distinguishes the normal cells and the test cells to transfer to an the input buffer 3 and then to store therein. The cells read from the input buffer 3 are supplied to an output buffer 5 in a destination output port by an ATM switch 4 and stored therein. An output buffer server 6 reads the cells from the output buffer 5 and separates the read cells into the normal cells and the test cells. The normal cells are transferred to the next stage in a normal manner. The test cells are supplied to a test cell receiving unit 7. The test cell receiving unit 7 tests each of the test cells supplied from the output buffer server 6 to determine the normality of cell conductivity.
However, the above conventional cell conductivity test apparatus has only the test cell generating unit 1 for sending out the test cells to the ATM switch 4 at the arbitrary rate. Therefore, there is the following problem.
In the ATM switching system, the test cells used to determine the normality of cell conductivity are accumulated in the input buffer 3 and the output buffer 5 in the ATM switching system in the same manner as the normal cell and then is processed. For this reason, if the test cells are merely flowed from the test cell generating unit 1 at a high rate, there is possibility that the normal cells are discarded for these test cells when the network is in a congestion state. That is, there is a case where the quality of service to the normal cells can not be guaranteed because of the influence of the test cells flowed at the high rate.
On the other hand, when the test to determine the normality of cell conductivity is performed using the test cells flowed at a very low rate, there is possibility that the ATM switching system is determined to be in a normal state, even if the ATM switching system has an intermittent fault in the communication path. Therefore, the cell conductivity test needs to be performed at a higher rate.